Stainless Steel Brake Piston, Two Required Per Caliper/Four Per Car. Diameter: 1.685" Applications: Series II E-Type Rear Series III E-Type Rear 420 Sedan Rear XJ-6 Series I Rear XJ-12 Series I Rear XJ-6 Series II to 2T.58038 Rear XJ-12 Series II to 2R.54650/2G.50651 Rear XJ-S, 1976 & 1977 Rear Note: These pistons do not have a wide retaining groove. (Read extended description.) As per Jaguar Part Number 11372. 316 stainless steel Manufactured by XKs Unlimited.XJ rear brake calipers are virtually the same from 1969 to mid-1993 but in the mid-’70s a larger groove was cut into the pistons to allow for a retaining ring for the rubber dust boots. A corresponding groove was cut into the caliper body. In addition, the mount flange was “fly-cut.” Calipers are usually interchangeable as units but the component parts are not. And, in some cases, later calipers will not fit an earlier differential, which can be difficult for hot rodders who don’t know the history of their rear suspension. Early calipers fit XJ-6 Series I, XJ-6 Series II to 2T.58038, XJ-12 Series I, XJ-12 Series II to 2R.54650/2G.50651, 1976 & 1977 XJ-S. Later calipers were used thereafter.